Microsoft Office may be the de facto productivity tool for millions of workers worldwide, but it's no monolith. Rather than a single, towering smooth-black Office, there's a whole Stonehenge..

Microsoft Office may be the de facto productivity tool for millions of workers worldwide, but it's no monolith. Rather than a single, towering smooth-black Office, there's a whole Stonehenge of options: Office on the iPhone, on iPad, Office on Android smartphones, Office on personal computers, Windows and macOS, Office with a handful of applications, Office with fist-fulls of apps.

But when you get down to it, there are really only two kinds of Office. One, labeled Office 2019, is the stand-alone suite that traces its roots back to the last century. The other, Office 365, is the subscription service that debuted in 2011.